1. Field of the Disclosure
The present disclosure relates to Magnetic Resonance Imaging (MRI) methods that provide imaging with reference to time. More particularly, the present disclosure relates to imaging with a flexible scan time during motion of a targeted organ.
2. Description of the Related Art
In general, a medical imaging device provides an image obtained from a patient. There are many types of medical imaging devices, such as ultrasonic diagnostic equipment, x-ray tomography equipment, magnetic resonance imaging equipment, and medical diagnostic equipment. In general, magnetic resonance imaging equipment functions provide superior contrast images of soft tissues of a human body, as well as provide various types of diagnostic information; thereby being a critical resource for diagnostic technology using medical images.
Generally, a magnetic resonance imaging device includes imaging equipment that diagnoses internal structures of a human body using the energy—already converted to a signal—induced from resonance reactions obtained by applying a constant rate of frequency and energy to nuclei of atoms of a patient while a predetermined magnetic field is applied to the patient.
There are unique challenges posed for providing high-resolution MRI when motion is involved. Such challenges are particularly present when, for example, performing an MRI of organs that have motion, such as coronary artery imaging, because of the complexities of both cardiac and respiratory motion.
Recent advances in both hardware and software MR technologies have permitted the performance of whole-heart imaging, specifically imaging for the visualization of the coronary arteries, so as to be performed in a clinically feasible scan time at both 1.5 T (tesla) and 3 T.
In practice, high-resolution imaging of a moving organ utilizes an ECG-gated k-space segmented acquisition strategy, which samples the 3D k-space volume only during the quiescent period of the motion of the organ such as the heart. For all of these known methods, a correctly timed trigger delay (TD) to synchronize the segmented k-space acquisition with the quiescent period of the cardiac cycle is essential.
Accordingly, a prior scout cine acquisition acquiring a series of images that are temporally spaced to acquire a series of images, is typically performed prior to the imaging to determine the optimal TD value for each individual, and subject who demonstrate heart-rate variability can present image quality degradation due to inaccurate TD timing errors.
An accurate timing determination for imaging can be difficult to ascertain in such subjects, as the heart rate can vary from beat to beat over the duration of a long scan duration, or change significantly in the presence or absence of breath-holding. In addition to the per-patient and physiological variability, the optimal period quiescent period with minimal motion for each artery branch may vary by anatomical position. Therefore, a single acquisition window may not necessarily be optimally timed for each coronary artery branch and region.
One way to attempt to overcome the aforementioned challenges is based on the incorporation of multiphase acquisition strategies with non-Cartesian sampling schemes into coronary imaging.
For example, a segmented 3D radial stack-of-stars acquisition approach generates four consecutive volumes at each temporal sub-window, and combines the sub-images to improve image quality.
Moreover, there have been studies exploring coronary acquisition over multiple temporal phases using k-space segmented strategies or high-resolution 3D cine approaches with radial or spiral sampling patterns. In all of the aforementioned multiphase 3D volumetric imaging approaches, the temporal window resolution is defined as the duration of each equally spaced temporal phase, and is not inherently designed for retrospective processing of any desired temporal subset within the acquisition window.
Accordingly, there remains a long-felt need in the art to provide a method that permits a retrospective processing of any desired temporal subset within the acquisition window.